Some embodiments described herein relate generally to apparatus and methods for microelectromechanical systems (MEMS) for density and mass flow sensing. More particularly, but not by way of limitation, some of the embodiments described herein relate to apparatus and methods for density and mass flow sensing using a balanced dual-tube MEMS resonator.
Mass flow and fluid density sensors using MEMS technology have been used in a variety of industries, including, for example, medical treatment systems such as drug infusion (delivery) and anesthetic delivery equipment, energy and fuel systems including fuel delivery systems and fuel cell systems such as direct methanol fuel cells (DMFC), chemical processing systems, and consumer goods. Coriolis-based microfluidic devices have provided accurate measurements of mass flow and fluid density. Some known Coriolis-based microfluidic devices include a micromachined tube supported above a substrate to have a free-standing portion. A drive mechanism is used to drive the free standing portion of the tube at or near resonance, while a sensing mechanism senses the Coriolis deflections of the resonating tube. The fluid density and the mass flow rate can therefore be deduced from the resonance frequency and the Coriolis deflections. The performance of these devices, however, is reduced due to mechanical losses resulting from attachment of the resonating tube to the substrate. Additionally, a relatively large packaging mass is used to dissipate the mechanical energy loss and isolate the resonating tube from external mechanical stress and vibration.
Accordingly, a need exists for apparatus and methods for a dual-tube MEMS design for density and mass flow sensing with efficient and controllable detection mechanisms.